How about you can trade perks for land mines, which you can place anywhere within a certain distance of a particular friendly field? The price and supply of mines can be managed based on arena balance so people don't go crazy...
To compensate for killshooter being abused with mines, a friendly should be able to detonate a mine if he runs over it, but it won't cause damage. That way a minefield can't be abused by luring enemy vehicles into it without the "friendly" driver knowing where the mines are. Drive over one of your own mines, and kaboom! The mine detonates causing no friendly damage but it would alert the enemy that there are mines around.
Have the mines expire and "come alive" only every 15 or so minutes so the server would only have to update people's clients with minefield lists every once in a while. Mines would expire off of the list automatically so the only realtime mine info would need to be which ones are actually detonated. That, plus limiting the number of active mines in the arena at any one time, might make the bandwidth problem associated with these things managable.
Either that, or make mines act like very very slow bullets
The mine owner's client is responsible for updating the host whenever a mine is detonated. That way the mine owner would be forced to remain nearby the mines in order to get player position updates and notice/report detonations. It would prevent abuse and over-use if the mine owner had to remain close to the mines otherwise they'd disappear.
